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An extended upper atmosphere around the extrasolar planet HD209458b
A Vidal-Madjar1, A Lecavelier Des Etangs, J-M Désert
1Institut d'Astrophysique de Paris, CNRS/UPMC, 98bis boulevard Arago, F-75014 Paris, France. alfred@iap.fr
Nature
|March 14, 2003
Summary
Astronomers detected atomic hydrogen escaping the gas giant HD209458b during transits. This finding, observed in the Lyman alpha line, suggests atmospheric escape beyond the planet's Roche limit.
Area of Science:
- Exoplanetary science
- Atmospheric physics
- Stellar astronomy
Background:
- HD209458b was the first exoplanet with observed transits, confirming its gas giant status.
- Previous observations detected only the lower atmosphere (neutral sodium) of HD209458b.
- Understanding exoplanet atmospheres is crucial for characterizing potentially habitable worlds.
Purpose of the Study:
- To detect and characterize the upper atmosphere of the exoplanet HD209458b.
- To investigate atmospheric escape mechanisms on gas giants.
- To utilize Lyman alpha line absorption during transits as a detection method.
Main Methods:
- Observing three transits of HD209458b across its host star.
- Measuring absorption in the stellar Lyman alpha line.
- Comparing observational data with atmospheric escape models.
Main Results:
- Detected atomic hydrogen absorption of 15 +/- 4% during HD209458b transits.
- The observed absorption indicates atmospheric escape beyond the Roche limit.
- This is the first detection of atomic hydrogen in HD209458b's atmosphere.
Conclusions:
- The upper atmosphere of HD209458b is actively escaping.
- Atomic hydrogen escape occurs beyond the planet's Roche limit.
- Lyman alpha observations are effective for studying exoplanet atmospheric escape.
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